1. Field of the Invention
The invention relates to a display device including a self-luminous light emitting element and a driving method thereof. More specifically, the invention relates to a pixel arrangement of the display device.
2. Description of the Related Art
In recent years, a display device having a light emitting element (self-luminous element) is actively developed. Such a display device is widely used as a display of a portable phone and a monitor of a computer by taking advantage of high resolution, thinness, and lightweight. In particular, such a display device has features as fast response, low voltage, low power consumption and the like, therefore it is expected to be applied to a wide range of devices including a new generation of a portable phone and a portable information terminal (PDA).
A light emitting element is also referred to as an organic light emitting diode (OLED) and has a structure that includes an anode, a cathode, and a layer including an organic compound (hereinafter referred to as an organic compound layer) sandwiched between the anode and cathode. A current flowing into the light emitting element and a luminance thereof have a fixed relation between them. The light emitting element emits light in accordance with a current flowing to the organic compound layer.
As a driving method of a display device having a light emitting element for displaying an image of multilevel gray scale, there are an analog driving method (analog gray scale method) and a digital driving method (digital gray scale method). They are different in the respect of a method for controlling emission and non-emission of a light emitting element.
In the analog driving method, a current flowing to the light emitting element is continuously controlled to display a gray scale. In the digital driving method, the light emitting element is controlled to be either ON state (a luminance is almost 100%) or OFF state (a luminance is almost 0%).
In the digital driving method, however, only two gray levels can be displayed as described above. Therefore, a driving method for displaying a multilevel gray scale image in combination with a time gray scale method or an area gray scale method is suggested. In the time gray scale display, for example, one frame is divided into subframes and a length of a light emitting period of each subframe is selectively determined to display a gray scale. Further, in the area gray scale method, a subpixel is provided in a pixel and its light emitting area is selectively determined to display a gray scale.
In the case of inputting a signal into a pixel, a voltage input method is typically employed. In the voltage input method, a luminance of a light emitting element is controlled by inputting a voltage to a gate electrode of a driving element as a video signal to be inputted to a pixel.
A driving method and a multilevel gray scale display method and the like of a display device as described above can be referred in Non-patent Document 1.
[Non-patent Document 1]
“Material technology and fabrication of elements regarding an organic EL display”, Technical Information Institute, 2002 January, p.179-196